Bachmann's Bundle's Unique Physiology: Reviewing How it Made an Atypical Flutter Even More Atypical

Abstract

A 69-year-old man with a history of previous ablation and cardiac surgery was found on cardiac electrophysiology study to have a macro-re-entrant left atrial flutter initially misdiagnosed as a micro-re-entrant right atrial tachycardia resulting from the unique conduction properties of Bachmann's bundle. (Level of Difficulty: Advanced.).

Keywords: BB, Bachmann’s bundle; Bachmann’s bundle; CS, coronary sinus; ECG, electrocardiogram; EP study; EP, electrophysiology; LA, left atrial; PPI-TCL, postpacing interval minus tachycardia cycle length; RA, right atrial; SVC, superior vena cava; SVT; SVT, supraventricular tachycardia; TCL, tachycardia cycle length; atypical flutter.

Graphical abstract

Figure 1

Electrocardiogram Demonstrating 2:1 Conduction of an Atrial Tachycardia or Slow Atypical Atrial Flutter

Figure 2

Coronary Sinus Catheter Placement Coronary sinus catheter placement confirmed supraventricular tachycardia with 2:1 conduction and an atrial cycle length of 352 milliseconds. Coronary sinus catheter placement also demonstrated a line of block along the coronary sinus catheter poles 7 to 8, consistent with previous external ablation performed during cardiac surgery.

Figure 3

Entrainment from the Distal Coronary Sinus Entrainment from the distal coronary sinus (coronary sinus 3-4), with a pacing cycle length of 340 milliseconds (tachycardia cycle length, 354 milliseconds) demonstrated the difference between the postpacing interval and the tachycardia cycle length to be 26 milliseconds, suggesting that the distal coronary sinus was within the circuit. Of note, pacing from this site captured both atrium and ventricle.

Figure 4

Activation Mapping Identifying a Site of Interest Within the RA Localized to the Anterior Superior Vena Cava Just Superior to the Cavoatrial Junction (A) Coherence mapping demonstrated typical distributive activation of a focal atrial tachycardia or micro–re-entrant flutter, originating from the site of interest (red) at the anterior superior vena cava and distributing throughout the right atrium (RA) and around the superior vena cava. (B) Entrainment suggested the site of interest to be within the tachycardia circuit. Of note, the green dots are within the circuit (difference between the postpacing interval and the tachycardia cycle length <30 milliseconds), the yellow areas are near the circuit (difference between the postpacing interval and the tachycardia cycle length, 30-50 milliseconds), and the brown dots are outside the circuit (difference between the postpacing interval and the tachycardia cycle length >50 milliseconds). CL = cycle length.

Figure 5

Entrainment From Right Atrial Site of Interest Entrainment with a pacing cycle length of 330 milliseconds (tachycardia cycle length, 352 milliseconds) from the right atrial site of interest (ablation distal) yielded a difference between the postpacing interval and the tachycardia cycle length of 6 milliseconds, a finding suggesting the site of interest to be within the tachycardia circuit.

Figure 6

Coherence Map of the RA Following Ablation Ablation lesions are demarcated by pink or red dots. Ablation performed within the right atrial site of interest did not affect the tachycardia. RA = right atrium; CL = cycle length.

Figure 7

Coherence Maps of the LA The maps show the (A) anterior and (B) posterior left atrium (LA) with associated entrainment sites, demonstrating a macro–re-entrant circuit involving the atrial roof, the location of the overlying Bachmann’s bundle. The green and blue dots are within the circuit (difference between the postpacing interval and the tachycardia cycle length <30 milliseconds), the yellow areas are near the circuit (difference between the postpacing interval and the tachycardia cycle length, 30-50 milliseconds), and the brown dots are outside the circuit (difference between the postpacing interval and the tachycardia cycle length >50 milliseconds). A postmaze residual leak along the right pulmonary vein carina was noted. CL = cycle length.

Figure 8

Coherence Map of the Posterior Wall The map shows an overlying line of ablation (red and pink dots) performed along the left atrial roof, which terminated the tachycardia. Additional lesions were performed along the right superior pulmonary vein antra to isolate the right-sided veins fully. LA = left atrium; CL = cycle length.

Figure 9

Activation Map of the Right and Left Atria The map shows ablation lesions (red dots) demonstrating the close proximity of the right atrial site of interest to the left atrium and highlighting the site to be along the course of Bachman’s bundle. RA = right atrium; LAT = local activation time.